Radical block polymerization of vinyl chloride. II. Synthesis and characterization of vinyl chloride block copolymers

Abstract

AbstractPeroxidized polypropylene has been used as a heterofunctional initiator for a two‐step emulsion polymerization of a vinyl monomer (M1) and vinyl chloride with the production of vinyl chloride block copolymers. Styrene, methyl‐, and n‐butyl methacrylate and methyl‐, ethyl‐, n‐butyl‐, and 2‐ethyl‐hexyl acrylate have been used as M1 and polymerized at 30–40°C. In the second step vinyl chloride was polymerized at 50°C. The range of chemical composition of the block copolymers depends on the rate of the first‐step polymerization of M1 and the duration of the second step; e.g., with 2‐ethyl‐hexyl acrylate block copolymers could be obtained with a vinyl chloride content of 25–90%. The block copolymers have been submitted to precipitation fractionation and GPC analysis. Noteworthy is the absence of any significant amount of homopolymers, as well as poly(M1)n as PVC. The absence of homo‐PVC was interpreted by an intra‐ and intermolecular tertiary hydrogen atom transfer from polypropylene residue to growing PVC sequences. The presence of saturated end groups on the PVC chains is responsible for the improved thermal stability of these block polymers, as well as their low rate of dehydrochlorination (180°C). Molecular aggregation in solution has been shown by molecular weight determination in benzene and tetrahydrofuran.